Viscose spinning process



United States Patent 3,324,216 VISCOSE SPINNING PROCESS Kagenobu Inoshita, Tsntomu Saijo, and Masaki Kaiiue, Shiga-ken, Japan, assignors to Toyo Spinning Co., Ltd., Osaka, Japan No Drawing. Filed May 10, 1963, Ser. No. 279,608 Claims priority, application Japan, May 16, 1962, 37/20,025, Patent 9,532 3 Claims. (Cl. 264-197) The invention relates to the production of novel artificial filaments and fibers, and particularly to the production of regenerated cellulose filaments and fibers having cotton-like properties from viscose.

It is one of the largest defects of usual artificial filaments and fibers from viscose that wet strength thereof is remarkably lower than that of cotton, .and it results from their low wet modulus. In order to overcome the defect and to produce artificial filaments and fibers having high wet modulus from viscose, various processes have been provided. Satisfactory products are not, however, obtained by those former processes. In Japanese Patent No. 172,865, etc., for example, there are described the processes for producing artificial fibers having high wet modulus by extruding viscose containing high degree of polymerization-cellulose into dilute acid baths. But knot strength of the fibers so obtained is too low, such as less than 1.2 g./d., to be suitable for textile uses. It is therefore necessary to treat them with alkaline medium as disclosed in Japanese Patent No. 188,036 to improve knot strength thereof. And in Japanese Patent No. 200,220, etc., there are described the processes for producing regenerated cellulose filaments having both improved wet strength and knot strength by extruding viscose containing coagulation modifiers such as monoamines into aqueous acidic solutions containing zinc sulfate of higher concentration. But wet elongation of the filaments thus obtained is much higher, such as more than 20%, than that of cotton (about 11%). Accordingly, they are unsuitable for staple fibers in spinning uses. As compared with those processes, this invention relates to a process for the production of novel regenerated cellulose filaments and fibers having high Wet strength, high knot strength and suitable wet elongation.

It is therefore an object of the present invention to provide a process for producing the novel filaments and fibers mentioned above.

It is a further object of the present invention to provide a process for producing regenerated cellulose filaments and fibers having cotton-like properties from viscose.

It is a still further object of the present invention to provide a novel and unique process for producing such filaments and fibers at a high speed from highly xanthated viscose.

These and other objects and advantages of the invention will be apparent from the following description and claims. I

We have now found that if highly xanthated viscose is extruded into a dilute acid bath and if slightly decomposed gel filaments withdrawn from the bath are regenerated in the air to a certain residual 'y value, filaments or fibers having high wet modulus and high knot strength may be obtained. Accordingly, the novel process of the invention consists of extruding viscose having a 7 value of at least about 50 through a spinneret into a dilute acid bath containing zinc sulfate and sodium sulfate to form gel filaments, withdrawing the filaments formed from the bath now that the residual 7 value is at least about 40, decomposing or regenerating the filaments thus withdrawn in the air so that the residual 7 value is between about 20 and about 35, and then stretching the filaments 3,324,216 Patented June 6, 1967 and before, after or during stretching, completing the regeneration thereof.

The term residual 7 value as applied herein to gel filaments or partially regenerated filaments is equal or corresponds, in the chemical nature, to 7 number of cellulose in viscose, and it is defined as:

7X213 or 16200 in which S is the dry weight of the completely regenerated filaments obtained from a sample, C is the total weight of the combined carbon disulfide in the sample and C is the total amount by gram molecule of the combined carbon disulfide in the sample. The method for quantitatively determining or analyzing this residual 7 value have been described in detail in US. Patent No. 3,084,- 021 (French Patent No. 128,692 or Belgian Patent No. 600,664) specification as residual xanthate ratio.

The viscose employed in this invention may be prepared from wood, cotton, linter or any of the other cellulosic materials. However, the present invention requires a highly xanthated extrusion having a gamma value of at least about 50. In the case of extruding viscose having a 7 value less than 50, it is difficult to withdraw gel filaments having a residual 'y value at least 40 from the spinning bath. When the gel filaments withdrawn have a residual 7 number less than 40, unsatisfactory products are obtained when the filaments are regenerated in the air to be a certain residual 7 number as mentioned hereinafter. On the other hand, it is generally difficult to extrude viscose when this 'y value is too high such as or more. For these reasons, the 7 number of viscose employed is required to be at least about 50, and is preferably about 55 to about 80. The viscose mentioned above may be prepared, for example, from cellulose xanthate obtained by reacting alkali cellulose with a higher or relatively higher amount of carbon disulfide and may be also prepared by adding an additional amount of carbon disulfide in usual viscose. There is no limit to the viscose except [for the 'y number mentioned above, but the viscose may contain preferably from about 3 to about 8% by weight cellulose having mean degree of polymerization at least about 300, particularly about 400 to about 700 and from about 2 to about 6% total alkali. The ball fall viscosity of the discose may be preferably at least about 30 seconds because it is diificult to form continuous filaments from the viscose having a viscosity less than 30 seconds by extruding it into a dilute acid bath. Particularly, the viscose employed in this invention may be highly xanthated having the cellulose concentration, the total alkali concentration and the degree of polymerization of cellulose, mentioned above, and from about 50 to about 500 second of the viscosity.

The spinneret employed in this invention may have holes having any diameter through which viscose is extruded and may be made of metal such as generally used. The spinneret made of glass may also be used to obtain better filaments and fibers.

In the first step of this invention the highly xanthated viscose mentioned before is extruded through the spinneret mentioned above into a dilute acid bath to form gel filaments. It is one of the main objects that such a bath is used so that the viscose extruded therein is formed into filaments. The behavior of the bath solution differs from that of usual spinning :bath solution in which viscose is regenerated. Therefore, it is necessary that the dilute bath solution possesses an ability to coagulate viscose at least partially, but it is preferable that the ability thereof to regenerate viscose is as Weak as possible. The preferable composition of the bath solution depends mainly upon the viscose to be extruded therein and spinning conditions such as spinning speed, bath temperature,

bath depth, etc., and may be suitably selected depending upon these factors. When the preferable viscose mentioned before is extruded, the bath may contain particularly from about 15 to about 35 g./l. sulfuric acid, from about 0.1 to about 3 g./l. zinc sulfate and at most about 100 g./l. sodium sulfate. Generally, there is not enough coagulation of the viscose in a bath containing less than 15 g./l. sulfuric acid and this causes breaking and sticking of the formed filaments. On the other hand, there is too strong a regeneration of the viscose in a bath containing more than 35 g./l. sulfuric acid so that the filaments suitable for the following step are not withdrawn therefrom unless the depth of the bath is made extremely short. There is insufiicient zinc sulfate to effect the formation of zinc xanthate-skin of the formed filaments in a bath containing less than 0.1 g./l. zinc sulfate and filaments having high knot strength are not obtained. On the other hand, there is formed a thick skin causing the sticking of the filaments together in a bath containing more than 3 g./l. zinc sulfate. If the dehydration of the formed filaments is effected in a bath containing more than 100 g./l. sodium sulfate then the withdrawn filament is not regenerated smoothly in the air. The spinning tube may be provided in the bath and the filaments formed may be passed therethrough. Particularly, it is advantageous to use the spinning tube to force the filaments at a high speed, and it is not very difficult, for example, to pass the filaments therethrough stably at 20 m./min. or higher. The temperature of the bath may be suitably selected between low temperatures and high temperatures. And the temperature is preferably from about 15 to about 35 C.; and is most advantageous at about room temperature heat-economically.

In the second step of this invention the filaments formed in the first step mentioned above are withdrawn from the bath under conditons wherein the residual y value remains at least about 40, particularly at least about 45. The withdrawing may be carried out by suitably selecting the length of the filaments running in the bath solution, that is, the depth or length of the bath employed. The depth or length depends upon not only viscose, bath solution but also withdrawing speed, and may be suitably selected depending upon these factors. When the preferable viscose mentioned before is extruded into the preferable dilute bath mentioned before and when the filaments formed are withdrawn therefrom at a speed from 15 to 50 m./min., the depth or length may be from about 5 to about 30 cm. If the depth be less than 5 cm., the coagulation of the withdrawn filaments is generally not enough. On the other hand, if it becomes more than 30 cm., the regeneration of the filaments is effected to excess. The coagulation modifier such as a monoamine may be present in the viscose and/ or the bath. In this case, the depth or length of the bath may be longer because the regeneration of viscose becomes slow, and thus the spinning operations become easier. But the zinc sulfate content in the bath may be kept to at most about 3 g./l. and it is necessary that a thin skin comprising zinc xanthate be formed over the filaments similarly to the case of the absence of modifiers. Accordingly up to this point, this invention differs from the production of high tenacity rayon by using acidic baths containing zinc sulfate of higher concentration to obtain filaments having thick skin. The filaments thus withdrawn have thin skin comprising zinc xanthate over the surface thereof and a core comprising slightly decomposed cellulose xanthate therein. Thus the filament formed is withdrawn from the dilute acid bath by suitable filament-advancing or filament-storaging means. The means for removing the excess bath liquid from the filaments such as a pin, a guide, rolls may be provided between the bath and the advancing or storaging means to slow the regenerating of the filament in the air mentioned below. In this manner, the filaments may be withdrawn from the bath at a speed at least about 15 m./min.

In the third step of this invention the filaments withdrawn in the second step are decomposed or regenerated in the air to a conditon so as to be between about 20 to about 35 in residual 7 number. The decomposition or regeneration in the air may be carried out in various manners, as, for example, on or around filaments-advancing means such as rolls, reels, drums and on or in filament-storaging means such as belts, plates, boxes. But it is preferable in the step to pass the withdrawn filaments around rolls or reels rotating in order to have continuous production. And it is also preferable to put the filaments during the regeneration under a tension as small as possible and at most 0.1 in drawing ratio to carry out the regeneration smoothly. At this point, two or more rolls rotating at a same peripheral speed in a same direction, for example, may be employed and the filaments may be passed around them continuously. The total time of the regeneration may be preferably at least about 5 seconds. If the time be less than 5 seconds, it is difiicult to obtain filaments or fibers having a core comprising fine structure to cause high wet modules. On the other hand, it is disadvantageous in practice to run the filaments over the preferable rolls mentioned above for a long time. Therefore, from about 5 seconds to about one minute is preferable in such manner. The temperature during the regenerating may be varied widely from lower to high, but is preferably near room temperature. The length of running filaments during the regeneration is decided chiefly from the time required, the tempearture employed and the running speed of the filaments. When the filaments are regenerated at room temperature during the preferable time mentioned above and when they are passed around the rolls at a speed from 15 to 50 m./min., the length may be about 2 to about 30 m. Before or during regenerating, a washing liquid may be applied to the filaments. At this time, the regeneration of the filaments is suitably slow and the dehydration of the filaments is smooth to easily obtain fibers or filaments having core comprising very fine structure to cause high wet modules. The liquid may be a more dilute acid solution than the liquid attached to the filaments. The liquid may contain, for example, from about 2 to about 10 g./l. sulfuric acid, at most 0.1 g./l. zinc sulfate and sodium sulfate of higher concentration. In this case, if the sulfuric acid content be less than 2 g./l., it is possible to cause sticking of the filaments together. Contrarily, if it be more than 10 g./l., there is no washing effect and it is possible to accelerate the regeneration because the liquid attached to the filaments contains generally approximately 10 g./l. sulfuric acid. The zinc sulfate content may be lower because it is already needless to promote zinc xanthate skin. The sodium sulfate content may be higher because there is promoted the dehydration of the filaments in presence of sodium sulfate to form the fine core. In this manner, the withdrawn filaments may be regenerated slowly in the air to a condition so as to be between about 20 to about 35 in the residual 'y number and the filaments having improved core described above are obtained. It is necessary to regenerate slowly in such a manner the filaments having a high residual '7 number to at most about 35 to form the improved core therein.

In the fourth step of this invention the filaments thus regenerated in the air are stretched. The stretching may be carried out in various manner, and for example, by passing them round a roll or rolls rotating at a certain speed and then collecting them on a roll or rolls rotating at a greater peripheral speed. The stretching ratio may be suitably selected depending upon the desiring properties of the final filaments or fibers. But the ratio may be preferable from about 1.4 to about 2.4 times of the original length of the filaments. Generally, if the filaments be stretched to a stretching ratio less than 1.6 times, it is difiic-ult to obtain the final filaments or fibers having high strength. On the other hand, if the filaments be stretched to a ratio more than 2.2 times it is possible that the final filaments or fibers will have low elongation and low knot strength. But in order to obtain the filaments or fibers for special uses, the stretching ratio out of the preferable range mentioned above may be taken.

Before, after or during the stretching mentioned above, the filaments thus obtained or the fibers obtained from the filaments, for example, by cutting are further regenerated to complete the regeneration. The completing the regeneration may be applied to any form of the filaments, and, for example, running filaments. caky filaments or filaments wound on bobbins. And the completing may be also applied to the fibers in various conditions, and, for example, fibers on a screen, fibers on a lattice, fibers on a belt and fibers in a box. The completing may be carried out in the air and may be also carried out in various regenerating baths. And the suitable bath employed may be an aqueous and may contain an acid or acids of lower concentration. Particularly, this may contain about 2 to about g./l. sulfuric acid. The temperature of the completing may be suitably selected from a wide range of temperatures. But it is preferable touse a warm or hot, for example, at least about 60 C., regenerating bath to complete the regeneration of the filaments or fibers in a shorter period. This is particularly advantageous when the filaments running at a high speed are treated. More particularly, the filaments may be stretched while passing through such a bath.

In accordance with this invention, the novel filaments or fibers having high wet strength, high knot strength and suitable wet elongation may be produced at a high speed, for example, at a collecting or winding-up speed at least about 30 m./min., particularly about 40- m./min. or higher. In some cases, the speed may be 100 m./min. or higher. Therefore, the speed is extremely higher than that of former processes in which dilute acid baths are used, and substantially equal to that of usual viscose process. In the present invention, the viscose may be extruded into the bath at room temperature and fully satisfactory filaments and fibers may be obtained thereby. Therefore, it is not always necessary in this invention that only the cold bath be used as in the former processes but also the warm bath may be used. Furthermore, the recovery of carbon disulfide produced is easily accomplished because the decomposing of cellulose xanthate is carried out mainly in the air, and there are advantages from the preparation and regeneration of the bath solution because the dilute solution is used. Thus, this invention is also a novel and advantageous process from industrial standpoints.

The filaments and fibers obtained by the present process have hard core comprising fine structure from effecting the slow regeneration of cellulose xanthane, and relatively soft skin from effecting the regeneration of zinc xanthate formed when extruding. Therefore, the filaments and fibers possess high wet modulus and high wet strength for the core, and also possess high knot strength and suitable wet elongation for the combination of the skin and the core. Particularly, the fibers and filaments produced under the preferable conditions described hereinabove have improved properties, for example, wet strength at least 2.6 g./d., wet elongation at least 10% and knot strength at least 1.6 g./ d. So the fibers and filaments are cotton-like and may be employed for various uses.

The invention will be more fully described by referring to the following examples, but it is understood that the invention is not limited thereto. The parts are by weight.

EXAMPLE I A dissolving wood pulp having 5.1 relative viscosity was steeped for 2 hours in an aqueous solution at C. containing 18.5% sodium hydroxide and the alkali cellulose was pressed until to be 2.8 times based on weight of the original pulp used. After shredding the alkali cellulose in a conventional manner at 25 to 30 C. for 2.5 hours, carbon disulfide in the amount of 50% based on weight of cellulose was added thereto, and the xanthation reaction was then allowed to proceed for minutes while elevating the temperature from 25 to 32 C. After the reaction, the cellulose xanthate was dissolved in 5 hours by adding thereto the predetermined amount of an aqueous dilute sodium hydroxide solution to give a viscose containing 5.0% cellulose and 3.1% total sodium hydroxide. After ripening, filtrating and deaerating, its ball fall viscosity was 398.4 seconds, its mean degree of polymerization of cellulose 630 and its 7 number 68.9.

The viscose was extruded through a spinneret having 2,000 holes of 0.05 mm. diameter into a bath at 25 C. containing 18 g./l. sulfuric acid, 0.5 g./l. zinc sulfate and 25 g./l. sodium sulfate to form the gel filaments.

The gel filaments were passed through a spinning tube having 17 cm. length with 10 l./min. bath solution, and then withdrawn from the bath onto a pair of godet rolls. The residual 7 number of the filaments when withdrawing was 54.7

The, rolls were both rotating at 25 m./min. peripheral speed in a same direction and the withdrawn filaments were passed thereon 4 rounds (corresponding to 6 m.) to be regenerated in the air only with the attached liquid thereof. The residual 7 number of the filaments when leaving the rolls was 30.7.

The filaments from the rolls were then passed into and through a hot bath at 98 C. containing 3 g./l. sulfuric acid, which length was 2 m. to complete the regeneration thereof.

The filaments, while passing through that bath, were stretched to 2.0 times of the original length and then collected by a roll rotating at 50 m./min. peripheral speed.

The filaments, after leaving the collecting roll, were washed with water, oiled and cut into staple fibers. The fibers after drying have the following properties:

Denier of individual fiber d 1.25

Dry breaking strength g./d 3.85

Dry breaking elongation percent 8.3

Wet breaking strength g./d 3.32

Wet breaking elongation percent 11.5

Dry knot strength g./d 1.80 EXAMPLE II The viscose prepared by the same operation as in Example I Was extruded through a spinneret having 50 holes of 0.05 mm. diameter into a bath at 25 C. containing 23 g./l. sulfuric acid, 0.8 g./l. zinc sulfate and 25 g./l. sodium sulfate, which depth was 18 cm., to form the gel filaments.

The gel filaments were withdrawn therefrom onto a pair of godet rolls rotating both at 35 m./min. peripheral speed in a same direction, The residual number of the filaments when withdrawing was 58.3.

The withdrawn filaments were passed on the rolls 5 rounds (corresponding to 8 m.) to be regenerated in the air only with the attached liquid thereof. The residual 7 number of the filaments when leaving the rolls was 27.4.

The filaments were then passed into and through a hot bath at 98 C. containing 3 g./l. sulfuric acid which length was 3 m. and stretched therein to 2.0 times of the original length by collecting them on a roll rotating at 70 m./min. peripheral speed.

The filaments, after leaving the collecting roll, were wound by centrifugal force, washed with water, oiled and dried. The properties of the filaments thus obtained are as follows:

Denier of individual filament d 2.40 Dry breaking strength g./d 3.47 Dry breaking elongation percent 9.2 Wet breaking strength g./d 3.12 Wet breaking elongation percent 12.4 Dry knot strength g./d 1.87

7 EXAMPLE III A shredded alkali cellulose prepared by the same operation as in Example I from a dissolving wood pulp having 4.6 relative viscosity was converted to cellulose xanthate -by adding thereto carbon disulfide in the amount of 60% based on weight of cellulose. The cellulose xanthate was dissolved by adding thereto the predetermined amount of an aqueous dilute sodium hydroxide solution to give a viscose containing 4.0% cellulose and 2.4% total sodium hydroxide. After ripening, filtrating and deaerating, the viscose had 106 seconds of ball fall viscosity, 490 of mean degree of polymerization of cellulose and 63.1 of 7 number.

The viscose was divided into two parts, and the one part was extruded through a spinneret made of metal having 2000 holes of 0.05 mm. diameter and the other through a spinneret made of glass having 2000 holes of the same diameter.

Both of the fibers obtained therefrom by the same manner as in Example I have the following properties:

Spinneret used Glass I Metal EXAMPLE IV In the viscose prepared by the same operation as in Example I, cyclohexylamine in the amount of 0.2% based on weight thereof was added, and the viscose containing cyclohexylamine was extruded into a bath at 25 C. containing 19 g./l. sulfuric acid, 70 g./l. sodium sulfate and 0.6 g./l. zinc sulfate which depth was 30 cm. to form the gel filaments.

The gel filaments having 53.3 residual 7 number were withdrawn from the bath onto a pair of godet rolls rotating at 26 m./min. peripheral speed in a same direction.

The filaments, while running between 7 m. round the rolls, were regenerated in the air only with the attached liquid thereof to 28.0 residual 7 number.

The filaments were then passed into and through a hot bath at 100 C. containing 3 g./l. sulfuric acid, and while passing therethrough were stretched to 2.1 times of the original length by collecting them on a roll rotating at 55 m./min.

The fibers, obtained by the same manner as in Example I from the filaments after leaving the collecting roll, have the following properties:

Denier of individual fiber d 1.25

Dry breaking strength g./d 3.61

Dry breaking elongation percent 10.5

Wet breaking strength g./d 3.07

Wet breaking elongation percent 13.9

Dry knot strength g./d 1.73

EXAMPLE V The gel filaments withdrawn by the same manner as in Example I were passed between 8 m. round a pair of rolls rotating at 25 m./min. in a same direction and a washing liquid at 20 C. containing g./l. sulfuric acid and 25 g./l. sodium sulfate was poured thereover while the passing to regenerate them slowly to 31.5 residual '7 number.

The fibers obtained by the same manner as in Example I from the filaments have the following properties:

Denier of individual fiber d 1.24 Dry breaking strength g./d 3.57 Dry breaking elongation percent 9.8 Wet breaking strength g./d 3.01 Wet breaking elongation percent 11.2 Dry knot strength g./d 2.17

8 EXAMPLE VI A dissolving wood pulp having 5.1 relative viscosity was steeped for 2 hours in an aqueous solution at 20 C. the original pulp used. After shredding the alkali cellulose was pressed until to be 2.7 times based on weight of the original pulp used. After shredding the alkali cellulose at 15 C. for 1 hour and without ageing them, carbon disulfide in the amount of 60% based on Weight of cellulose was added thereto, and the xanthation reaction was then allowed to proceed for 3.5 hours while elevating the temperature from 15 to 25 C. After the reaction, the cellulose xanthate was dissolved in 3 hours by adding thereto the predetermined amount of an aqueous dilute sodium hydroxide solution at 10 C. to give a viscose containing 5.0% cellulose and 3.0% total sodium hydroxide. After ripening, filtrating and deaerating, the viscose had 286.4 seconds of ball fall viscosity, 480 of mean degree of polymerization of cellulose and 63.3 of 'y number.

The viscose was divided into two parts, and each of them was extruded through a spinneret having 2000 holes of 0.05 mm. diameter into a bath at 25 C. containing 18 g./l. sulfuric acid, 0.5 g./l. zinc sulfate and 25 g./l. sodium sulfate to form the gel filaments.

The gel filaments were passed through a spinning tube having 12 cm. length, and then withdrawn from the bath onto a pair of godet rolls rotating at 50 m./min. peripheral speed. The residual 7 number of the filaments when withdrawing was 56.3.

The withdrawn filaments were passed thereon 4 rounds (corresponding to 6.8 m.) to be regenerated in the air only with the attached liquid thereof. The residual 7 number of the filaments when leaving the rolls was 31.5.

One of the filaments thus obtained was then passed into and through a dilute acid bath at 45 C. and the other into and through another dilute acid at 25 C. Both of the bath contained 3 g./l. sulfuric acid and had 2 m. length. Each of the filaments, while passing through each of these baths, was stretched to 2.0 times of the original length by collecting it on a roll rotating at m./min. peripheral speed.

Each of the fibers obtained by the same manner as in Example I has the following properties:

EXAMPLE VII A cellulose xanthate prepared by the same operation as in Example VI, except that the pressed alkali cellulose was shredded at 30 C. for 1 hour, was dissolved in 3 hours by adding thereto the predetermined amount of an aqueous dilute sodium hydroxide solution at 10 C. to give a viscose containing 4.0% cellulose and 2.4% total sodium hydroxide. After ripening, filtrating and deaerating, the viscose had 118.6 seconds of ball fall viscosity, 550 of means degree of polymerization of cellulose and 67.8 of 7 number.

The viscose was divided into two parts, and each of them was withdrawn by the same manner as in Example VI, except to use a spinning tube having 17 cm. length. The residual 'y number of the filaments when withdrawing was 53.5.

The withdrawn filaments were passed thereon 3 rounds (corresponding to 5.2 m.) to be regenerated in the air only with the attached liquid thereof. The residual 'y number of the filaments when leaving the rolls was 29.6.

Each of the filaments was stretched and regenerated completely in the regenerating bath as in Example VI, except for the temperature of the bath used. Namely, the one thereof was 40 C. and the other 25 C.

Each of the fibers obtained from such filaments by the same manner as in Example I has the following properties:

Temperature of regenerating bath Denier of individual fiber, d 1. 21 1. 20 Wet breaking strength, g./d 3. 67 3. 59 Wet breaking elongation, percent 9. 9 9. 7 Dry knot strength, g./d 1. 55 1. 57 Dry knot elongation, percent 4 1 4.

EXAMPLE VIII The filaments having 53.5 residual 7 number, obtained by being regenerated in the air as in Example VII, were stretched in the air to 20 times of the original length by collecting them on a roll rotating at 100 m./min. peripheral speed, and then laid upon a moving belt to be completed the regeneration thereof.

The filaments thus obtained were cut into the staple fibers, and the fibers were washed with water, oiled on a lattice conveyor. The fibers after drying have the following properties:

Denier of individual fiber d 1.23

Wet breaking strength g./d 3.56

Wet breaking elongation percent 9.9

Dry knot strength g./d 1.63

Dry knot elongation percent 4.0

EXAMPLE IX The viscose prepared by the same operation as in EX- ample III was extruded through a spinneret having 1000 holes of 0.05 mm. diameter into a canal-shaped bath at 25 C. containing 21 g./l. sulfuric acid, 1.2 g./l. zinc sulfate and 25 g./l. sodium sulfate, which length was 18 cm., to form the gel filaments.

The gel filaments were withdrawn therefrom into the air, by passing them onto a pair of Nelson-type rolls rotating at 80 m./min. peripheral speed. The residual 'y number of the filaments when withdrawing was 58.5.

The withdrawn filaments were passed thereon in 35 m. and regenerated only with the attached liquid thereof to be 30.0 of the residual 7 number.

The filaments thus regenerated in the air were passed into and through a hot bath at 100 C. containing 3 g./l. sulfuric acid, and while passing through the bath, stretched to 2.0 times of the original length by collecting them on a roll rotating at 160 m./min. peripheral speed. The filaments were then washed, oiled, dried by a conventional manner, and wound on a bobbin.

The properties of the filaments thus obtained are as follows:

Denier of individual filament d 1.20 Dry breaking strength g./d 3.24 Dry breaking elongation percent 10.1 Wet breaking strength g./d 2.65 Wet breaking elongation percent 12.3 Dry knot strength g./d 1.7

It is seen from the above description that the objects of this invention are well fulfilled by the process described. The description is intended to be illustrative only, and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention, as defined in the appended claims.

What we claim is:

1. A process for producing regenerated cellulose filaments which comprises extruding a viscose having a gamma number of at least about 50 into a dilute acid coagulating bath containing about 15-35 g./l. of sulfuric acid, about 0.13 g./l. of zinc sulfate and at most about 100 g./l. of sodium sulfate and maintained at a temperature of about 1535 C. to form gel filaments, withdrawing the filaments from said coagulating bath while the residual gamma number is at least about 40, regenerating the withdrawn filaments in air until the residual gamma number is about 20.35, and then stretching the filaments and completing the regeneration in a regeneration bath containing about 2-15 g./l. of sulfuric acid and maintained at a temperature of at least about C.

2. A process as claimed in claim 1, wherein the viscose contains cellulose of at least about 300 mean degree of polymerization degree, about 3 8% by weight of cellulose and about 26% by weight of total alkali.

3. A process as claimed in claim 1 wherein the filaments are allowed to stand in the air for about 5 seconds to about 1 minute, and are substantially not stretched in the air.

References Cited UNITED STATES PATENTS 2,607,955 8/1952 Drisch et a1. 1854 2,611,928 9/1952 Drisch et a1. 1854 2,699,983 1/1955 Merion et al 1854 3,084,021 4/1963 Morimoto 264-197 X 3,108,849 10/1963 Owashi et al. 3,128,147 4/1964 Kenyon et al. 3,139,467 6/1964 Drisch et a1. 264198 FOREIGN PATENTS 1,266,099 5/1961 France.

956,803 4/ 1964 Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner. MORRIS LIEBMAN, Examiner.

C. B. HAMBURG, A. L. LEAVITT, J. H. WOO,

Assistant Examiners. 

1. A PROCESS FOR PRODUCING REGENERATED CELLULOSE FILAMENTS WHICH COMPRISES EXTRUDING A VISCOSE HAVING A GAMMA NUMBER OF AT LEAST ABOUT 50 INTO A DILUTE ACID COAGULATING BATH CONTAINING ABOUT 15/35 G./L. OF SULFURIC ACID, ABOUT 0.1-3 G./L. OF ZINC SULFATE AND AT MOST ABOUT 100 G./L. OF SODIUM SULFATE AND MAINTAINED AT A TEMPERATURE OF ABOUT 15-35*C. TO FORM GEL FILAMENTS, WITHDRAWING THE FILAMENTS FROM SAID COAGULATING BATH WHILE THE RESIDUAL GAMMA NUMBER IS AT LEAST ABOUT 40, REGENERATING THE WITHDRAWN FILAMENTS IN AIR UNTIL THE RESIDUAL GAMMA NUMBER IS ABOUT 20.35, AND THEN STRETCHING THE FILAMENTS AND COMPLETING THE REGENERATION IN A REGENERATION BATH CONTAINING ABOUT 2-15 G./L. OF SULFURIC ACID AND MAINTAINED AT A TEMPERATURE OF AT LEAST ABOUT 60*C. 